1

IDENTIFICATION OF CT NUMBER (NCT) AT THE PRIMER AREA (GTV) OF

ASTROCYTOMA AND CERVICAL CANCER

Lovina Wijayanti1, Unggul P. Juswono

1, Sri Martono

2, Ubaidillah

1

1Department of Physics, Faculty of Matemathics and Natural Sciences,

University of Brawijaya – Malang, East Java, Indonesia 2 Department of Radiology, Saiful Anwar General Hospital – Malang, East Java, Indonesia

Email: lovinaliu@gmail.com

Abstract-Treatment planning system (TPS) is a fundamental procedure in external radiotherapy. One of TPS

procedure is cancer segmentation using the results of a CT-Scan image. Cancer area is segmented in each slice

of CT -scan image by an expert radiation oncologist. This procedure is very dependent on the experience,

expertise of the doctor and requires a high level of accuracy. Therefore, this study aimed to identify and define

CT Numbers (NCT) that can explain quantitatively about how radiation oncologist perform cancer segmentation

based on qualitative observation on CT-Scan result. Determination of CT Numbers (NCT) was done by using

descriptive statistical analysis on the CT Numbers (NCT) that was obtained from the CT scan DICOM file

(Digital Imaging and Communications in Medicine) of a patient with astrocytomas and two patients with stage

III cervical cancer. The results showed that NCT = +31 HU to +38 HU indicates the presence of a tumor on the

left side of the astrocytomas patient (PX-1) head. NCT = +7 HU to +45 HU in the case of cervical cancer patient

(PY-1) shows the hypodense area that indicates the cancer area. Whereas in patient PY-2 was obtained NCT = +6

HU to +49 HU that indicates the homogeneous density in the area of cervical cancer spreading.

Key Words : CT Number, DICOM, CT-Scan, Astrocytoma, cervical cancer, Bilangan CT, DICOM, CT-Scan,

astrositoma, cervical cancer, external radiotherapy

1. INTRODUCTION

Cancer is one of the leading causes of

morbidity and mortality in Indonesia,

amounting to 111 people per 100.000

population (WHO, 2014). In November 2014,

there were 8,990 cancer patients in Saiful

Anwar General Hospital consisting of 5,058

breast cancer cases, 2,316 cases of cervical

cancer and 1,616 cases of nasopharyngeal

cancer [2]. In addition, cases of brain tumors

is also a quite dangerous because it can affect

people at any age and is generally difficult to

diagnose at an early stage [3].

Cervical cancer is the second type of

cancer that is a most deadly disease for

women worldwide after breast cancer cases

[4]. The absence of specific symptoms or

signs of early stage cervical cancer causes it is

often detected only upon entering an

advanced [3].

Astrocytoma is one type of glioma

brain tumor that is most common in adults at

the middle ages, 30-40 years [5].

Astrocytomas have a tendency to become

glioblastoma (stage IV astrocytoma) when it

was not given by an effective treatment [6].

Characteristics of early stage (I and II)

astrocytoma is slowly grow that will cause the

patient did not experience specific symptoms

until the tumor has a large size and cause

symptoms that can be felt clearly, for

example, epileptic seizures and headache [3].

One of effective technique for cancer

treatment is external radiotherapy [7]. The

success of external radiotherapy procedure is

influenced by the accuracy of defining the

location and area of cancer spread. The results

of volume and location determination of the

cancer is useful to determine the magnitude

and direction of the radiation dose to be

administered to the patient [8]. Cancer

volume definition is done carefully by a

radiation oncologist based on qualitative

observations on the results of a CT-scan

patients [9].

The process of defining the primary

cancer area (Gross Tumor Volume, GTV) and

the area of spread of cancer, namely CTV

(Clinical Target Volume) and PTV (Planning

Target Volume) performed by a specialist in

each slice axial CT scan of the patient.

Defining the cancer area is very dependent on

the experience and expertise of the doctor. In

addition, the process of defining the area of

cancer performed by expert doctors also

require quite a lot of time because it had to be

done in each axial slice of the patient's body

into the location where the cancer was

2

diagnosed. Therefore, we need a method to

help semiautomatic segmentation cancer area

[10].

This study aims to identify the range of

CT Number (NCT) which may represent the

area of primary cancer and its spread. It also

can explain the results of cancer diagnosis by

a radiation oncologist through a quantitative

approach. CT Number (NCT) is a value which

represents the attenuation of material. NCT has

a value that varies depending on the type of

material and the quality of X-ray beam used

in the procedure of CT-Scan [11]. The results

of CT Number identification in the area of

cancer can be used to determine the

differences between the constituent cells of

cancerous tissue and the normal tissue located

around the cancer.

2. METHODS

This research was conducted in

Department of Radiology, Saiful Anwar

General Hospital and Computation

Laboratory Department of Physics, University

of Brawijaya, Malang.

The equipment used in this study

include a computer with an Intel Core i3 1.7

GHz, 4GB RAM, 500GB hard drivers that are

equipped with Windows 8 operating system,

compiler NetBeans IDE 8.0.1, the application

HU Inspector, SPSS v20, and Agnosco

DICOM viewer.

The data used to identifying the value

of NCT in the case of astrocytoma is DICOM

CT-Scan of 5 patients comprising a control

patients (PX-1) who suffered from

astrocytoma tumor and 4 reference patients

(PX-2, PX 3, PX -4, and PX-5) which is not

an astrocytoma patients. Patients selected by

criteria of age (46.2 ± 6.3) years old, female,

and underwent head CT scan procedure on the

part of the brain without contrast medium

injection. While in the case of cervical cancer,

used two DICOM data of patients with stage

III cervical cancer by contrast medium

injection, the PY-1 patients (36 years) and

patients PY-2 (56 years).

Procedures for the identification and

evaluation of the distribution of CT Number

(NCT) conducted by HU Inspector application

that was created by author using Java

language and NetBeans IDE 8.0.1 compiler.

Identification of CT Number was done in the

area of cancer in accordance with the

radiation oncologist's diagnosis.

The defining of cancer area is done through

CT-Scan image overlapping technique of the

patient who had been given cancer contour

(GTV, CTV and PTV) by radiation oncologist

using HU Inspector application.

Figure 1 An Example of defining procedures to

make contours of cancerous area based on the CT-

Scan image that had been diagnosed by a radiation

oncologist. (A) The CT-Scan image of PX-1

(patients with astrocytoma) patients head (looks

inferior) were reconstructed using HU Inspector

application. (B) Overlapping contour area of

cancer on CT-scan image (Figure 1A). (C)

Defining the tumor area with HU Inspector

application in accordance with the contour cancer

that had been made by a radiation oncologist.

NCT value of each pixel from the CT-

Scan image in the area of cancer that has been

defined in accordance with procedures shown

in Figure 1 will be displayed by HU Inspector

in the form of numerical data. NCT values

obtained are then analyzed using descriptive

statistical techniques (mean, median, mode,

standard deviation) with SPSS v20 to

determine the frequency distribution and the

range of CT Number (NCT) that dominate the

cancer area of patients PX-1, PY-1 and PY-2,

While the evaluation of the CT Number

distribution conducted qualitatively in each

slice of CT scan result using certain colors

represent a certain range of NCT value. NCT

value was classified into color classes by

using a formulation derived from Sturges

interval rule.

3

3. RESULTS

The results of this research will discuss

the value of CT numbers (NCT) which

dominates the primary astrocytoma tumor

area (GTV area) of patients PX-1, a primary

cervical cancer area (GTV area) of patients

PY-1, and the cervical cancer area (CTV area)

of patients PY -2.

3.1 Astrocytoma Case NCT range value in the area of GTV,

CTV, and PTV of astrocytoma patients (PX-

1) in Figure 2 is the result of NCT value

identification contained in eight sequential

axial slices (1st up to 8

th) of PX-1 patient's

head that is being the location of

astrocytomas. The slices of 9th is the result of

NCT identification in the area of GTV, CTV,

and PTV as a whole from the 1st up to 8

th

axial slices.

Figure 2 shows that the value of NCT on

GTV area of astrocytoma patients (PX-1) has

a mean value greater than the CTV and PTV

area. Thus, GTV area of astrocytoma patients

is dominated by the range values of NCT = (35

± 4) HU tend to have a greater density than

the surrounding tissue which can be proved

by the results of windowing result (Figure 3).

Figure 3 is a CT-Scan image display of PX-1

head which has been given gradation settings

(windowing) with a minimum value NCT =

+31 HU and maximum value NCT = +38 HU

in accordance with the format Monochrome 2.

Brain area that have a value of NCT < +31 HU

is displayed as an area with a dark (black)

color, while the area with NCT = (+ 31≤ NCT

<+39) HU appear grayish color according to

the magnitude value of NCT in each pixel of

CT-Scan image. While the area with NCT

values> +38 HU displayed as white areas.

The windowing results on PX-1 CT-

Scan image (Figure 3) shows that the range of

values NCT = +31 HU up to +38 HU can be a

marker for the location of the primary area

(GTV) of astrocytomas that are seen as an

area with relatively greater density (lighter

color) compared to the surrounding area.

Color NCT (HU)

HU 8 +37 s.d +38

HU 7 +35 s.d +36

HU 6 +33 s.d +34

HU 5 +31 s.d +32

20.00

22.00

24.00

26.00

28.00

30.00

32.00

34.00

36.00

38.00

40.00

42.00

0 1 2 3 4 5 6 7 8 9 10

CT

Nu

mb

er (

HU

)

Number of slice location on the PX-1 patients' head

GTV CTV PTV

Figure 3 Comparison of color distribution

between normal and astrocytoma patients.

Figure 4 The windowing result on four

sequential slices of PX-1 CT-Scan image

Figure 2 NCT range value of astrocytoma

patients (PX-1)

More hypodense area that GTV area

Cranial bone

4

Kelas HU 5 to HU 7 Kelas HU 8 to HU 10

NCT value evaluation on the results of a

CT scan result of patients PX-1 (Astrocytoma)

and PX-2 who is a normal patients (without

brain tumors) conducted qualitatively by

comparing the distribution pattern of color

that represent the NCT value of each pixel in a

slice of CT-Scan image (Figure 4). Figure 4

shows that a normal brain tissue (without

astrocytoma) near the cranial bone (orange

circle) is also has a value of NCT = +31 HU up

to +38 HU (Class of HU5 to HU8) same as

with NCT value in the GTV of astrocytoma in

PX-1 patients.

Figure 4.a indicates appearance of a

relatively symmetrical distribution of color in

both parts of the right brain and the left brain

areas of PX-2 patients compared with the PX-

1 patients. Symmetry properties of the brain

in patients PX-2 is a characteristic of the

normal anatomical structure of the human

brain [12].

The asymmetry of brain tissue that was

found on the left side of PX-1 brain is

characterized by the presence of GTV area

(Figure 4.b) which has the same NCT value

with the brain tissue near the cranial bone

(NCT = +31 HU up to +38 HU). Identical value

of NCT in the area of GTV and brain tissue

near to PX-1 patients’ cranial bone can be

explained by a histological approaches about

the constituent cell of astrocytoma tumor.

Astrocytoma tumor cells was derived

from astrocytes, which are glial cells exist

in the brain. Glial cells are as numerous as

neurons that is 50% of brain volume and it

has function to protect and give the

nutrients for nerve cells [13]. CT Number values are specific to a

particular tissue depends on the capabilities of

the X-ray attenuation by cell components

making up a tissue [14]. Therefore, the

similarity of the color distribution of the

identification results NCT = +31 HU up to +38

HU in the area of the astrocytoma tumor

(GTV) and surrounding areas of the brain

near with cranial bone in PX-1 patients, which

represents the structure of the gray substance

(Figure 5) shows that the astrocytoma tumor

cells in patients PX-1 is derived from

astrocytes cells which are in substance grisea.

3.2 Cervical Cancer Case

The results of NCT identification in the

case of cervical cancer indicate a difference in

the homogeneity of the X-ray attenuation,

although it was found that PY-1 and PY-2

have the similiar NCT range value, that are

NCT = +7 HU up to +45 HU in patients PY-1

and NCT = +6 HU up to +49 HU in patients

PY-2.

Figure 6 Qualitative observations which

represent the NCT value distribution in the cervical

area of PY-1 patients

Color NCT (HU)

HU 11 +43 up to +44

HU 10 +41 up to +42

HU 9 +39 up to +40

HU 8 +37 up to +38

HU 7 +35 up to +36

HU 6 +33 up to +34

HU 5 +31 up to +32

Color NCT (HU)

HU 10 +72 up to +84

HU 9 +59 up to +71

HU 8 +46 up to +58

HU 7 +33 up to +45

HU 6 +20 up to +32

HU 5 +7 up to +19

1. Cranial bones

2. Dura mater

3. Subarachnoid space

4. Gray matter

5. White matter

Figure 5 Brain structure comparison of PX-1

patients with the structure of the normal human

brain without astrocytoma. (a) The inset picture

is a normal brain area (without tumor) of PX-1,

(b) normal brain structure [1], (c) color

identification results for a range of values NCT =

+31 HU up to +44 HU in brain of PX-1 (axial

slices no.3, looked inferior).

5

NCT value that dominates the center of

the GTV area in cervical cancer patients (PY-

1) is NCT = +7 HU up to HU +45 (Class of

HU5 to HU 7). While the color grade HU 8

until HU 10 (NCT = +46 HU up to +84 HU)

dominates the edge of the GTV area of PY-1

as shown in Figure 6.

NCT range value differences in cervical

patients PY-1 indicate the presence of

heterogeneity attenuation (attenuation) X-ray

between the center of the cervix and cervical

edge. The edge of the cervix tends to absorb

more X-rays than the center of the cervix

which is characterized by the value of NCT on

the edge of the cervix area which is relatively

large compared with the central part of the

cervix. Whereas qualitative observations on

the color distribution in cervical area of PY-2

patients were more likely to indicate the

presence of X-ray attenuation homogeneity

which is marked by the distribution of color

on the class of HU 9 until HU 12 (NCT = +17

HU up to +49 HU) that is homogeneous

throughout the area surrounding the cervix

(Figure 7).

NCT range value identification results in

patients with cervical cancer (PY-1 and PY-2)

showed that the degree of NCT range value

homogeneity on the cervical area can be used

as an indication of the spread of cervical

cancer. The central part of PY-1 patients’

cervix which has a relatively lower value of

NCT (hipodensity) than the edge of the cervix

is an indication that cervical cancer is still in

the middle area of the cervix. While the

homogeneity of the distribution value of NCT

= +6 HU to +49 HU entire area surrounding

the PY-2 patients’ cervix (Figure 7) is an

indication that the entire area of the cervix of

PY-2 is the area of cervical cancer has been

spreading.

The lower NCT value is a consequence

of cell damage due to cancer. Normal blood

vessels are strong and not easily fragile, while

the blood vessels that grow in the cancer cells

are fragile and easily broken [3]. Rupture of

blood vessels in cancer cells are characterized

by bleeding out through the patient's vagina

will cause a shortage of cancer cells

vascularization. Lack of vascularization in

cancer cells resulting in cancer cells undergo

necrosis and become less active in absorbing

material contrast compared with normal cells

[15].

4. CONCLUSION

Results of NCT range value

identification in astrocytoma tumor area and

cervical cancer that were obtained in this

study has been able to provide quantitative

explanations on the results of cancer diagnosis

that has made by radiation oncologist. In the

case of astrocytoma patients (PX-1), NCT =

+31 HU up to +38 HU is an indication that

the astrocytma tumor in PX-1 has a radiation

absorption characteristics similar to cells of

astrocytes in the gray substance. NCT = +7 HU

up to +45 HU in PY-1 patients showed the

hypodensity area that indicate the presence of

cervical cancer. Whereas in PY-2 patients was

obtained a NCT = +6 HU up to +49 HU

showing the homogeneity of cervical cancer

that become a indication that the cervical

cancer potentially to spread toward the pelvic

wall.

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HU 11 +28 up to +38

HU 10 +17 up to +27

HU 9 +6 up to +16

HU 8 -5 up to +5

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